1. Field of the Invention
This invention generally relates to a voltage level shifter, and more particularly to a latchable voltage level shifter with a high voltage flip-flop.
2. Description of Related Art
The electronic circuits usually have to latch the data into the flip-flop according to the predetermined timing sequence and then shift the voltage level of the latched data for subsequent processing. The source drive circuit of the liquid crystal display (LCD) is one example.
FIG. 1 is the block diagram of a traditional LCD source drive circuit. Referring to FIG. 1, the driver circuit is one of the source drive circuits in the LCD. After by the source drive circuit 100 processes the display data DATA, the source drive signal 151 will be obtained. The source drive signal 151 will be sent to one of the source channel of the LCD panel (not shown). The LCD panel receives the source drive signals from each source channel to display the image.
Generally, to correctly latch the display data of the source channels, the line latch 100 will latch the display data DATA according to the first timing sequence DIO to obtain the display data 111. To make sure that the source drive circuit of each source channel can output the source drive signal 151 simultaneously, the prior art uses line latch 120 to latch the display data 111 according to the timing sequence LD to obtain the display data 121; then the voltage level shifter 130 shifts the display data 121 with a lower voltage level of to become the display data 131 with a higher voltage level. The D/A converter 140 converts the digital display data 121 to an analog source drive signal 141. To enhance the driving ability of the source drive signal 141, the operational amplifier 150 amplifies the source drive signal 141 and outputs the source drive signal 151.
However, when designing the traditional voltage level shifter, the designer has to consider the channel length/width ratio of the MOSFET. Because the drafting effect in the semiconductor manufacturing process is almost unavoidable, it becomes difficult to control the channel length/width ratio. In addition, in the traditional design, the designer has to take the line latch and the voltage level shifter into account, which causes that the source drive circuits of the LCD with multi-channels occupy more layout areas and thus increase the power consumption and the production cost.